Adhesive film for semiconductor, lead frame with adhesive film for semiconductor and semiconductor device using the same

ABSTRACT

An adhesive film for semiconductor, which has a three-layer structure consisting of a support film having each face coated with an adhesive layer, each adhesive layer containing (A) a heat resistant thermoplastic resin having a glass transition temperature of 130 to 300° C., a water absorption of 3% by weight or less and a squeeze length of 2 mm or less, (B) an epoxy resin and (C) a trisphenol compound as an epoxy resin-curing agent; a lead frame with adhesive film; and a semiconductor device wherein the lead frame with adhesive film is bonded to a semiconductor element.

TECHNICAL FIELD

This invention relates to an adhesive film for semiconductor, a leadframe with adhesive film for semiconductor and a semiconductor deviceusing the same.

BACKGROUND ART

Despite recent enlargement of semiconductor chips because of increasesin functions and storage capacity, the packages housing them need smallexternal shapes due to restrictions in designs of printed wiring boardsand demands for downsized electronic apparatuses. To meet such tendency,there have been proposed some new mounting systems applicable both forsemiconductor chips of increased density and for high-density mounting.Particularly, LOC structures proposed for memory elements, wherein leadsare bonded on chips, can improve efficiency in interconnection of chipsand wire bonding and shorten interconnecting lines, thereby speeding upsignal transmission and downsizing packages.

In the new mounting system, bonding interfaces exist between differentmaterials, such as semiconductor chips and lead frames, and theirbonding reliability strongly influences the reliability of semiconductorpackages. Not to mention to bonding workability and reliabilitytolerable to the processing temperatures during packaging, such bondingreliability as to tolerate to moisture absorption and wet heat andprevent package cracking during solder reflow for mounting on substratesis a matter of importance.

Paste adhesives or adhesives applied to heat resistant base materialshave been used for bonding them. An example is a hot-melt type adhesivefilm using polyimide resins (Japanese Patent Application Non-examinedPublication Nos. 5-105850 (1993), 5-112760 (1993) and 5-112761 (1993)).However, bonding with hot-melt type adhesives needs very hightemperatures due to the high Tg of the adhesive resins, and tends tothermally damage semiconductor chips and adherents, particularly copperlead frames. Lowering the Tg gives adhesive films having low temperatureadhesive property, but causes the problem of package cracking becausethe adhesive resins having lowered heat resistance reliability andincreased elasticity cannot relieve the heat stress applied betweenchips and lead frames by the heat history during solder reflow formounting on substrates.

DISCLOSURE OF INVENTION

This invention provides an adhesive film for semiconductor, which can bebonded at low temperatures in semiconductor devices.

This invention further provides a lead frame with adhesive film forsemiconductor produced by punching the adhesive film for semiconductorto stick it to a prescribed position of a lead frame.

This invention further provides an extremely reliable semiconductordevice containing a lead frame and a semiconductor element bondedtogether by the adhesive film for semiconductor.

The inventors of this invention have tried to develop adhesive films forsemiconductor satisfying both low temperature adhesive property andreflow cracking resistance of semiconductor devices, with the resultthat they have found that the above-described problems can be solved byforming adhesive layers from an adhesive, which contains a heatresistant thermoplastic resin having specific properties, an epoxy resinand a trisphenol compounds as an epoxy resin-curing agent, and completedthis invention.

Accordingly, this invention relates to an adhesive film forsemiconductor (the adhesive film of the first invention), which has athree-layer structure consisting of a support film having each facecoated with an adhesive layer, each adhesive layer containing (A) a heatresistant thermoplastic resin having a glass transition temperature of130 to 300° C., a water absorption of 3% by weight or less and a squeezelength of 2 mm or less, (B) an epoxy resin and (C) a trisphenol compoundas an epoxy resin-curing agent.

This invention further relates to an adhesive film for semiconductor(the adhesive film of the second invention), which has a three-layerstructure consisting of a support film having each face coated with anadhesive layer, each adhesive layer containing (A) a heat resistantthermoplastic resin having a glass transition temperature of 130 to 300°C., (B) an epoxy resin and (C) a trisphenol compound as an epoxyresin-curing agent, wherein the adhesive film having the three-layerstructure has a water absorption of 3% by weight or less and a squeezelength of 2 mm or less.

This invention further relates to a lead frame with adhesive film forsemiconductor, comprising a lead frame and the adhesive film forsemiconductor stuck to the lead frame.

This invention further relates to a semiconductor device, containing alead frame and a semiconductor element which are bonded to each otherwith the adhesive film for semiconductor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of the adhesive film for semiconductor ofthis invention.

FIG. 2 is a sectional view of a semiconductor device using the adhesivefilm for semiconductor of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The heat resistant thermoplastic resin (A) to be used in the adhesivefilm of the first invention has a glass transition temperature of 130 to300° C., a water absorption of 3% by weight or less and a squeeze lengthof 2 mm or less, and is therefore preferably a polyimide resin or apolyamide resin. Herein, the terms polyimide resins mean resins havingimido groups, such as polyimide resins, polyamideimide resins,polyesterimide resins and polyetherimide resins.

If the glass transition temperature deviates from the above-describedrange, or the water absorption is more than 3% by weight, or the squeezelength is more than 2 mm, the semiconductor devices produced by usingthe adhesive film for semiconductor of this invention may have poorreflow cracking resistance.

The glass transition temperature of the heat resistant thermoplasticresin to be used in this invention is preferably 180 to 250° C. Thewater absorption is preferably 2.5% by weight or less, more preferably2.0% by weight or less. The squeeze length is preferably 1 mm or less,more preferably 0.5 mm or less.

Herein, the water absorption of the heat resistant thermoplastic resinmay be obtained by measuring the weight of a film of the heat resistantthermoplastic resin dried at 130° C. for one hour, immersing the driedfilm in distilled water of 25° C. for 24 hours and then measuring theweight of the film, and estimate water absorption from the followingequation: {(weight after immersion−weight before immersion)/weightbefore immersion}×100(%). The squeeze length of the heat resistantthermoplastic resin is determined by pressing with heat a 19 mm×50 mm×25μm thick film of a heat resistant thermoplastic resin at 350° C. under apressure of 3 MPa for one minute, and measuring the length of the resinsqueezed out perpendicularly from the center of the longer side of theoriginal film.

The heat resistant thermoplastic resin (A) used in the adhesive film ofthe second invention has a glass transition temperature of 130 to 300°C. for the same reason as in the first invention. Also, the examples andpreferred examples of the usable heat resistant thermoplastic resin (A)are the same as those for the first invention. The second inventionprescribes that the adhesive film of the three-layer structureconsisting of a support film having each face coated with an adhesivelayer, not the heat resistant thermoplastic resin, has a waterabsorption of 3% by weight or less and a squeeze length of 2 mm or less.The preferable ranges thereof are the same as those for the firstinvention.

The water absorption of the adhesive film of the second invention may beobtained by the same method as that for the first invention except thatthe adhesive film of three-layer structure is used in place of the filmof the heat resistant thermoplastic resin (A). The squeeze length of theadhesive film of the second invention may be obtained by cutting theadhesive film of three-layer structure instead of the heat resistantthermoplastic resin (A) into the same sizes (19 mm×50 mm), andconducting the same measurement as that for the first invention.

The adhesive film for semiconductor of the present invention preferablyhas both the characteristics defined in the first invention and thecharacteristics defined in the second invention.

Hereinafter, the adhesive film of the first invention, the adhesive filmof the second invention, the lead frame with adhesive film forsemiconductor and the semiconductor device using the same will bedescribed.

The epoxy resin to be used in this invention may be any one having atleast two epoxy groups per molecule. Examples are the compounds of thefollowing formulae (1) to (3):

wherein Z₁ is a divalent organic group, Z₂ is a tetravalent organicgroup and Z₃ is a trivalent organic group.

Examples of the epoxy resins include bisphenol A diglycidyl ether,bisphenol F diglycidyl ether, bisphenol AD diglycidyl ether, bisphenol Sdiglycidyl ether, 2,6-xylenol diglycidyl ether, hydrogenated bisphenol Adiglycidyl ether, 1,4-cyclohexane dimethanol diglycidyl ether,oxydiphenol diglycidyl ether, diglycidyl ethers of ethylene oxide-adductof bisphenol A, diglycidyl ethers of propylene oxide-adduct of bisphenolA, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidylether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidylether, glycidyl ethers of phenol novolak resins, glycidyl ethers ofcresol novolak resins, glycidyl ethers of naphthalene resins,trifunctional glycidyl ethers, tetrafunctional glycidyl ethers, glycidylethers of dicyclopentadiene phenolic resins, glycidyl esters of dimeracids, trifunctional glycidylamines, tetrafunctional glycidylamines,glycidylamines of naphthalene resins, polysulfide-modified epoxy resinsand polybutadiene-modified epoxy resins. They may contain monofunctionalepoxides.

Preferred epoxy resins have an epoxy equivalent weight of 50 to 600,more preferably 150 to 500.

The epoxy resin-curing agent contained in the adhesive layers of thisinvention is a trisphenol compound having three hydroxyphenyl groups permolecule. Preferred examples of the trisphenol compounds are representedby the following general formula (a).

In formula (a), R₁ to R₁₀ are each independently hydrogen, an alkylgroup of 1 to 10 carbon atoms, a cycloalkyl group of 5 to 10 carbonatoms, phenyl group or hydroxyl group. R₅ is preferably hydrogen, analkyl group of 1 to 10 carbon atoms, a cycloalkyl group of 5 to 10carbon atoms or phenyl group, more preferably hydrogen or an alkyl groupof 1 to 10 carbon atoms. D is a tetravalent organic group. Examples ofthe tetravalent organic group D are as follows.

In general formula (a), preferred examples of ≡D—R₅ are as follows.

Examples of the trisphenol compounds include4,4′,4″-methylidenetrisphenol,4,4′-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol,4,4′,4″-ethylidinetris[2-methylphenol],4,4′,4″-ethylidinetrisphenol,4,4′-[(2-hydroxyphenyl)methylene]bis[2-methylphenol],4,4′-[(4-hydroxyphenyl)methylene]bis[2-methylphenol],4,4′-[(2-hydroxyphenyl)methylene]bis[2,3-dimethylphenol],4,4′-[(4-hydroxyphenyl)methylene]bis[2,6-dimethylphenol],4,4′-[(3-hydroxyphenyl)methylene]bis[2,3-dimethylphenol],2,2′-[(2-hydroxyphenyl)methylene]bis[3,5-dimethylphenol],2,2′-[(4-hydroxyphenyl)methylene]bis[3,5-dimethylphenol],4,4′-[(2-hydroxyphenyl)methylene]bis[2,3,5-trimethylphenol],4,4′-[(2-hydroxyphenyl)methylene]bis[2,3,6-trimethylphenyl],4,4′-[(3-hydroxyphenyl)methylene]bis[2,3,6-trimethylphenol],4,4′-[(4-hydroxyphenyl)methylene]bis[2,3,6-trimethylphenol],4,4′-[(2-hydroxyphenyl)methylene]bis[2-cyclohexyl-5-methylphenol],4,4′-[(3-hydroxyphenyl)methylene]bis[2-cyclohexyl-5-methylphenol],4,4′-[(4-hydroxyphenyl)methylene]bis[2-cyclohexyl-5-methylphenol],4,4′-[(3,4-dihydroxyphenyl)methylene]bis[2-methylphenol],4,4′-[(3,4-dihydroxyphenyl)methylene]bis[2,6-dimethylphenol],4,4′-[(3,4-dihydroxyphenyl)methylene]bis[2,3,6-trimethylphenol],4-[bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)methyl]-1,2-benzenediol,4,4′-[(2-hydroxyphenyl)methylene]bis[3-methylphenol],1,3,3-tris(4-hydroxyphenyl)butane,4,4′-[(2-hydroxyphenyl)methylene]bis[2-isopropylphenol],4,4′-[(3-hydroxyphenyl)methylene]bis[2-isopropylphenol],4,4′-[(4-hydroxyphenyl)methylene]bis[2-isopropylphenol],2,2′-[(3-hydroxyphenyl)methylene]bis[3,5,6-trimethylphenol],2,2′-[(4-hydroxyphenyl)methylene]bis[3,5,6-trimethylphenol],4,4′-[(2-hydroxyphenyl)methylene]bis[2-cyclohexylphenol],4,4′-[(3-hydroxyphenyl)methylene]bis[2-cyclohexylphenol],4,4′-[1-[4-[1-(4-hydroxy-3,5-dimethylphenyl)-1-methylethyl]phenyl]ethylidene]bis[2,6-dimethylphenol],4,4′,4″-methylidinetris[2-cyclohexyl-5-methylphenol],4,4′-[1-[4-[1-(3-cyclohexyl-4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bis[2-cyclohexylphenol],2,2′-[(3,4-dihydroxyphenyl)methylene]bis[3,5-dimethylphenol],4,4′-[(3,4-dihydroxyphenyl)methylene]bis[2-isopropylphenol],2,2′-[3,4-dihydroxyphenyl)methylene]bis[3,5,6-trimethylphenyl],4,4′-[(3,4-dihydroxyphenyl)methylene]bis[2-cyclohexylphenol] and α, α′,α″-tris(4-hydroxyphenyl)-1,3,5-triisopropylbenzene.

The adhesive to be used in the adhesive film of this invention containspreferably 1 to 100 parts by weight, more preferably 2 to 50 parts byweight of the epoxy resin and preferably 0.02 to 120 parts by weight,more preferably 0.1 to 80 parts by weight, further preferably 1 to 20parts by weight of the epoxy resin-curing agent, both relative to 100parts by weight of the heat resistant thermoplastic resin.

If more than 100 parts by weight of the epoxy resin and more than 120parts by weight of the epoxy resin-curing agent are used, filmformability may be aggravated. If less than 1 parts by weight of theepoxy resin and less than 0.02 parts by weight of the epoxy resin-curingagent are used, bonding failure may occur due to aggravated lowtemperature adhesive property.

The adhesive to be used in the adhesive film of this invention mayoptionally contain cure accelerators, which may be any one commonly usedto cure epoxy resins. Examples include imidazoles, dicyanediamidederivatives, dicarboxylic acid dihydrazides, triphenylphosphine,tetraphenylphosphonium tetraborate, 2-ethyl-4-methylimidazoletetraphenylborate and1,8-diazabicyclo(5,4,0)undecene-7-tetraphenylborate. These may be usedindividually or in combination of two or more. In view of storagestability, the amount of the cure accelerators used, if any, isgenerally 50 parts by weight or less, for example, 0.01 to 50 parts byweight, preferably 20 parts by weight or less, relative to 100 parts byweight of the epoxy resin.

To improve adhesion to the support film, coupling agents may be added tothe adhesive to be used in the adhesive film of this invention, forexample silane coupling agents, such asγ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, aminosilane,γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane,methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane,hexamethyldisilazane, γ-anilinopropyltrimethoxysilane andvinyltrimethoxysilane, titanate coupling agents, such as isopropyltriisostearoyl titanate, isopropyl trioctanoyl titanate, isopropyltridodecylbenzenesulfonyl titanate and isopropyltris(dioctylpyrophosphate) titanate, and aluminum coupling agents, suchas acetalkoxyaluminum diisopropylate.

In view of heat resistance and adhesion to lead frames, the amount ofthe coupling agents added is preferably 0.5 to 20 parts by weight, morepreferably 2 to 10 parts by weight, relative to 100 parts by weight ofthe heat resistant thermoplastic resin.

The support film to be used in this invention is preferably aninsulating heat resistant resin film, such as polyimides, polyamides,polysulfones, polyphenylenesulfides, polyetheretherketones,polyallyrates and polycarbonates. The thickness of the support film isnot particularly limited, and in general, it is preferably 5 to 200 μm,more preferably 20 to 75 μm.

It is desirable to use support films having glass transitiontemperatures higher than the adhesive to be used in this invention,preferably 200° C. or higher, more preferably 250° C. or higher. Thesupport film preferably has a water absorption of 3% by weight or less,more preferably 2% by weight or less.

The support film to be used in this invention is preferably aninsulating heat resistant resin film having a glass transitiontemperature of 250° C. or higher, a water absorption of 2% by weight orless and a thermal expansion coefficient of 3×10⁻⁵/° C. or less,particularly preferably a polyimide film.

The support film preferably has surfaces treated before its use toincrease the bonding strength between the support film and the adhesivelayers and prevent the peeling between the support film and the adhesivelayers.

The method of surface treatment for the support film may be any one, forexample, a chemical treatment, such as alkali treatment or silanecoupling treatment, a mechanical treatment, such as sand mat treatment,plasma treatment or corona treatment, and a treatment best adapted tothe kind of adhesive used may be chosen. Chemical treatments and plasmatreatment are particularly suited for treating the support film to beused in this invention.

Any method may be used to form the adhesive layers on the support filmmay be any one, and in general, the heat resistant thermoplastic resin,the epoxy resin and the epoxy resin-curing agent, which form theadhesive layers, are dissolved in an organic solvent to give an adhesivevarnish. The solvent used may be any one, which uniformly dissolves ormixes the above-described materials, such as dimethylformamide,dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide,diethylene glycol dimethyl ether, toluene, benzene, xylene, methyl ethylketone, tetrahydrofuran and dioxane.

The adhesive varnish obtained as above are applied to the support film,and then heated to remove solvents and to perform imidation. Thisprocedure is carried out twice, to give an adhesive film of three-layerstructure.

Temperatures at which solvents can be removed will suffice for heatingthe support film coated with the adhesive varnish to remove solvents.

Any coating method may be employed, for example, roll coating, reverseroll coating, gravure coating, bar coating and comma coating. Coatingmay also be performed by passing the support film through the adhesivevarnish, but control of thickness will be difficult.

Each adhesive layer formed on the support film is preferably 1 to 75 μmthick, more preferably 10 to 30 μm thick. Adhesive layers thinner than 1μm are inferior in adhesive property and productivity, and those thickerthan 75 μm increase the production cost.

Thus obtained adhesive film has a structure as shown in FIG. 1. The filmmay be used as an adhesive for semiconductor. In FIG. 1, 1 indicatessupport film, and 2 indicates adhesive layer.

Highly reliable lead frames attached with adhesive film can be producedreadily with high yields by using the adhesive film of this invention.For example, the adhesive film of this invention is cut into film piecesof prescribed sizes, which are then bonded to lead frames. The adhesivefilm may be cut by any method, so far as it may be cut into prescribedshapes accurately. In view of workability, it is preferable to use apunching die to cut the adhesive film and bond the punched film piecedirectly to a lead frame. The bonding temperature is generally 150 to300° C., preferably 200 to 250° C. Bonding temperatures lower than 150°C. cannot give sufficient bonding strength, and those higher than 300°C. may thermally aggravate the adhesive layers or oxidize lead frames.Bonding pressure is generally 0.1 to 20 MPa, preferably 0.3 to 10 MPa.Bonding pressures lower than 0.1 MPa may not give sufficient bondingstrength, and those higher than 20 MPa may squeeze out the adhesive fromthe prescribed position, lowering the dimensional accuracy. The bondingtime is not limited so far as bonding can be accomplished at theabove-described bonding temperatures and bonding pressures, and in viewof efficiency, it is preferably 0.3 to 60 seconds, more preferably 0.5to 10 seconds.

Highly reliable semiconductor devices can be produced easily with goodworkability and high yields by using the adhesive film of thisinvention.

The adhesive film of this invention may be used in place of silver pastein packages of conventional structure using silver paste, or in multichip packages containing plural chips and packages of COL (Chip On Lead)structure, particularly suitably in semiconductor devices of LOC (LeadOn Chip) structure. Because of the ability of low temperature bonding,it is suitable for semiconductor devices of various LOC structures,including not only the conventional TSOP (Thin Small Outline Package)structure but also QFP (Quad Flatpack Package) structure and stuckstructure.

For example, in cases where the lead frame with adhesive film producedas described above is used, a semiconductor devices of LOC structure canbe produced by bonding a semiconductor chip to the adhesive layer on theside to which the lead frame is not bonded, curing the adhesive film,connecting the lead frame with the semiconductor chip by gold wire orthe like, and then sealing them by transfer molding a molding material,such as epoxy resins.

The temperature at which semiconductor chips are bonded is generally 150to 300° C., preferably 200 to 250° C. Bonding temperatures lower than150° C. cannot give sufficient bonding strength, and those higher than300° C. cause the problems of thermal degradation of adhesive layers oroxidation of lead frames. Bonding pressure is generally 0.1 to 20 MPa,preferably 0.3 to 10 MPa. Bonding pressure lower than 0.1 MPa cannotgive sufficient bonding strength, and those higher than 20 MPa maysqueeze out the adhesive from the prescribed positions to lower thedimensional accuracy and brake semiconductor chips.

Pressing time is not limited so far as bonding can be accomplished atthe above-described bonding temperatures and bonding pressures, and inview of efficiency, it is preferably 0.3 to 60 seconds, more preferably0.5 to 10 seconds.

Curing temperature is generally 150 to 200° C., preferably 170 to 180°C. Curing temperatures lower than 150° C. are insufficient for curing,and those higher than 200° C. may cause oxidation of lead frames. Curingtime is generally 15 to 75 minutes, preferably 30 to 60 minutes. Curingtimes less than 15 minutes are insufficient for curing, and those longerthan 75 minutes decrease the working efficiency. Alternatively, sealingmaterial-curing step following to the sealing by transfer molding themolding material, such as epoxy resins, can double as the curingtreatment for the adhesive film.

This invention will be described in more detail with reference to thefollowing Examples, which however are not to be construed to limit thescope of the invention.

EXAMPLES 1 TO 4 AND COMPARATIVE EXAMPLE 1

The following polyamideimides A to C were used as heat resistantthermoplastic resins to prepare varnishes Nos. 1 to 5 (Nos. 1 to 4: forExamples 1 to 4 according to this invention, respectively, No. 5: forComparative Example 1) of the compositions as shown in Tables 2 and 3.

The polyamideimides A, B and C used were synthesized as follows.

Synthesis of Polyamideimide A

Into a 5-liter four-necked flask equipped with a thermometer, a stirrer,a nitrogen inlet tube and a fractionating column was placed 210 g (0.5moles) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane in nitrogenatmosphere, and dissolved in 1200 g of N-methyl-2-pyrrolidone. Thesolution was cooled to −10° C., and 105.3 g (0.5 moles) of trimelliticacid monochloride was added thereto, while keeping the temperature below−5° C. After the trimellitic acid monochloride was dissolved, 76 g oftriethylamine was added, while keeping the temperature below 5° C. Afterstirring for one hour at room temperature, reaction was carried out at180° C. for 9 hours to complete imidation. The resulting reactionsolution was poured in methanol, to separate a polymer. After drying,the polymer was dissolved in dimethylformamide, and poured into methanolto separate the polymer again. It was then dried under reduced pressure,to give a purified powdery polyamideimide A. 60 g of the powderypolyamideimide A was dissolved in 200 g of N-methyl-2-pyrrolidone, togive an adhesive varnish. The varnish was cast on a glass plate to 90 μmthick, dried at 100° C. for 10 minutes, peeled off from the glass plate,secured to an iron frame and dried at 200° C. for 10 minutes and at 300°C. for 10 minutes, to give a 25 μm thick film of an adhesive. The filmhad a glass transition temperature of 230° C., a water absorption of1.8% by weight and a squeeze length of 0.2 mm.

Synthesis of Polyamideimide B

Into a 5-liter four-necked flask equipped with a thermometer, a stirrer,a nitrogen inlet tube and a fractionating column were placed 143.5 g(0.35 moles) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane and 37.2 g(0.15 moles) of 1,3-bis(aminopropyl)tetramethyldisiloxane in nitrogenatmosphere, and dissolved in 1200 g of N-methyl-2-pyrrolidone. Thesolution was cooled to −10° C., and 105.3 g (0.5 moles) of trimelliticacid monochloride was added thereto, while keeping the temperature below−5° C. After the trimellitic acid monochloride was dissolved, 76 g oftriethylamine was added, while keeping the temperature below 5° C. Afterstirring for one hour at room temperature, reaction was carried out at180° C. for 9 hours to complete imidation. The resulting reactionsolution was poured in methanol, to separate a polymer. After drying,the polymer was dissolved in dimethylformamide, and poured into methanolto separate the polymer again. It was then dried under reduced pressure,to give a purified powdery polyamideimide B. 60 g of the powderypolyamideimide B was dissolved in 200 g of N-methyl-2-pyrrolidone, togive an adhesive varnish. The varnish was cast on a glass plate to 90 μmthick, dried at 100° C. for 10 minutes, peeled off from the glass plate,secured to an iron frame and dried at 200° C. for 10 minutes and at 300°C. for 10 minutes, to give a 25 μm thick film of an adhesive. The filmhad a glass transition temperature of 190° C., a water absorption of1.5% by weight and a squeeze length of 0.4 mm.

Synthesis of Polyamideimide C

Into a 5-liter four-necked flask equipped with a thermometer, a stirrer,a nitrogen inlet tube and a fractionating column were placed 61.5 g(0.15 moles) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane and 86.8 g(0.35 moles) of 1,3-bis(aminopropyl)tetramethyldisiloxane in nitrogenatmosphere, and dissolved in 1200 g of N-methyl-2-pyrrolidone. Thesolution was cooled to −10° C., and 105.3 g (0.5 moles) of trimelliticacid monochloride was added thereto, while keeping the temperature below−5° C. After the trimellitic acid monochloride was dissolved, 76 g oftriethylamine was added, while keeping the temperature below 5° C. Afterstirring for one hour at room temperature, reaction was carried out at180° C. for 9 hours to complete imidation. The resulting reactionsolution was poured in methanol, to separate a polymer. After drying,the polymer was dissolved in dimethylformamide, and poured into methanolto separate the polymer again. It was then dried under reduced pressure,to give a purified powdery polyamideimide C. 60 g of the powderypolyamideimide C was dissolved in 200 g of N-methyl-2-pyrrolidone, togive an adhesive varnish. The varnish was cast on a glass plate to 90 μmthick, dried at 100° C. for 10 minutes, peeled off from the glass plate,secured to an iron frame and dried at 200° C. for 10 minutes and at 300°C. for 10 minutes, to give a 25 μm thick film of an adhesive. The filmhad a glass transition temperature of 100° C., a water absorption of1.0% by weight and a squeeze length of 3.5 mm.

TABLE 1 Glass Water Heat resistant transition absorption Squeezethermoplastic temperature (% by length resin (° C.) weight) (mm)Polyamideimide A 230 1.8 0.2 Polyamideimide B 190 1.5 0.4 PolyamideimideC 100 1.0 3.5

The letters in Tables 2 and 3 indicate the followings.

YDCN-702: cresol novolak epoxy resin (epoxy equivalent weight: 220)produced by Tohto Kasei Kabushiki Kaisha

ESCN-195: cresol novolak epoxy resin (epoxy equivalent weight: 200)produced by Sumitomo Chemical Co., Ltd.

N865-E: bisphenol novolak epoxy resin (epoxy equivalent weight: 208)produced by Dainippon Ink Chemicals, Inc.

BEO-60E: ethylene oxide-adduct bisphenol epoxy resin (epoxy equivalentweight: 373) produced by Shin-Nippon Rikagaku Kabushiki Kaisha

DEM-100: cyclohexane dimethanol epoxy resin (epoxy equivalent weight:155) produced by Shin-Nippon Rikagaku Kabushiki Kaisha

TrisP-TC: trisphenol novolak (OH equivalent weight: 160) produced byHonshu Kagaku Kabushiki Kaisha, chemical name: α, α′,α″-tris(4-hydroxyphenyl)-1,3,5-triisopropylbenzene; formula (a1)

TrisP-PA: trisphenol novolak (OH equivalent weight: 141) produced byHonshu Kagaku Kabushiki Kaisha, chemical name:4,4′-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol;formula (a2)

TrisP-PHBA: trisphenol novolak (OH equivalent weight: 97) produced byHonshu Kagaku Kabushiki Kaisha, chemical name:4,4′,4″-methylidinetrisphenol; formula (a3)

TrisP-HAP: trisphenol novolak (OH equivalent weight: 102) produced byHonshu Kagaku Kabushiki Kaisha, chemical name:4,4′,4″-ethylidinetrisphenol; formula (a4)

DMAc: dimethylacetamide

DMF: dimethylformamide

NMP: N-methyl-2-pyrrolidone

TABLE 2 (Composition) Varnish number Ingredient No. 1 No. 2 No. 3 No. 4Heat A B A B resistant 100 100 100 100 thermoplastic resin (wt part)Epoxy resin YDCN-702 ESCN-195 N-865 BEO-60E (wt part) 10 20 25 20 Epoxyresin- TrisP-TC TrisP-PA TrisP-PHBA TrisP-HAP curing agent 7.3 14.1 11.75.5 (wt part) Solvent DMAc NMP DMF DMAc (wt part) 500 350 450 500

TABLE 3 (Composition) Varnish number Ingredient No. 5 Heat C resistant100 thermoplastic resin (wt part) Epoxy resin YDCN-702 (wt part) 10Epoxy resin- TrisP-TC curing agent 7.3 (wt part) Solvent DMAc (wt part)500

Each of these varnishes was applied to each face of a 50 μm thickchemically surface treated polyimide film (trade name: UPILEX S,produced by Ube Industries, Ltd.) to 100 μm thick, and both sides of thefilm were dried separately at 100° C. for 10 minutes and 200° C. for 10minutes, to give adhesive films for semiconductor having a 25 μm thickadhesive layer on each side as shown in FIG. 1 (Examples 1 to 4: usingvarnishes Nos. 1 to 4 respectively, Comparative Example 1: using varnishNo. 5).

The adhesive films of Examples 1 to 4 and Comparative Example 1 wereexamined for film formability, adhesive property and reflow crackingresistance. The results are listed in Table 4.

The water absorption and squeeze length of the adhesive films ofthree-layer structure produced in Examples 1 to 4 and ComparativeExample 1 were determined. The results are listed in Table 5.

Evaluation Method for Film Formability

The adhesive films produced as described above were checked for thestickiness of their adhesive layers. Non-sticky ones were rated as“good”, and sticky ones as “inferior”.

Evaluation Method for Low Temperature Adhesive Property

Lead frames attached with adhesive film were produced by punching outeach adhesive film with a punching die into strips, which were placed ona 0.15 mm thick copper alloy lead frame to apply them to 0.2 mm wideinner leads arranged at 0.2 mm intervals, and then bonded by pressing at250° C. for 3 seconds with a pressure of 3 MPa. The lead frames attachedwith adhesive film were dropped from a level 2 m high on the ground toexamine for the falling off of the adhesive film strips. Adhesive filmsthe strips of which did not fall off were rated as “good”, and those thestrips of which fell off were rated as “inferior”.

Evaluation Method for Reflow Cracking Resistance

To the exposed adhesive layer of each of the lead frames attached withadhesive film that were produced for the evaluation for adhesiveproperty, were bonded a semiconductor element by pressing at 250° C. for3 seconds with a pressure of 3 MPa, and then the lead frame and thesemiconductor element were connected by wire-bonding with gold wires andsealed by transfer molding a biphenyl epoxy resin molding material(trade name: CEL-9200, produced by Hitachi Chemical Co., Ltd.) andpost-curing at 175° C. for 6 hours, to give semiconductor devices asshown in FIG. 2. In FIGS. 2, 3 indicates adhesive film, 4 indicatessemiconductor element, 5 indicates lead frame, 6 indicates sealingmaterial, 7 indicates bonding wire and 8 is bus bar.

The semiconductor devices thus obtained were allowed to stand for 168hours in a high temperature-high humidity atmosphere of 85° C. and 85%RH, and then subjected twice to a treatment comprising passing themthrough an IR reflow furnace the temperature of which was controlled sothat the surfaces of the semiconductor devices were kept at 240° C. for20 seconds and cooling them by allowing to stand at room temperature.Thereafter, they were observed for the presence of cracks. Those free ofcracks were rated as “good”, and those cracked were rated as “inferior”.

TABLE 4 Results of Evaluation for the Properties of Adhesive Films Comp.Example Example Example Example Example Properties 1 2 3 4 1 Film goodgood good good good formability Low good good good good good temperatureadhesive property Reflow good good good good inferior crackingresistance

TABLE 5 Water Absorption and Squeeze Length of Adhesive Film ofThree-Layer Structure (support film: 100 μm, adhesive layer: 25 μm each)Water Absorption of Squeeze Length of Adhesive Film Adhesive Film (wt %)(mm) Example 1 1.8 0.3 Example 2 1.7 0.4 Example 3 1.8 0.3 Example 4 1.70.5 Comp. 1.4 3.8 Example 1

Examples 1 to 4 possessed the elements required by this invention, andwere excellent in film formability, low temperature adhesive propertyand reflow cracking resistance.

Comparative Example 1 did not satisfy the Tg and squeeze length of theheat resistant thermoplastic resin required by this invention, and wasinferior in reflow cracking resistance.

Industrial Applicability

The adhesive film for semiconductor of this invention can be bonded atlow temperatures, and is particularly useful for the production of leadframes attached with adhesive film using copper lead frames.Semiconductor devices produced by using the lead frames attached withadhesive film have excellent reflow cracking resistance and highreliability.

What is claimed is:
 1. An adhesive film for semiconductor, which has athree-layer structure consisting of a support film having each facecoated with an adhesive layer, each adhesive layer containing (A) a heatresistant thermoplastic resin having a glass transition temperature of130 to 300° C., a water absorption of 3% by weight or less and a squeezelength of 2 mm or less, (B) an epoxy resin and (C) a trisphenol compoundas an epoxy resin-curing agent.
 2. The adhesive film for semiconductorof claim 1, wherein each adhesive layer contains 100 parts by weight ofthe heat resistant thermoplastic resin (A), 1 to 100 parts by weight ofthe epoxy resin (B) and 0.02 to 120 parts by weight of the epoxyresin-curing agent (C).
 3. The adhesive film for semiconductor of claim1, wherein the heat resistant thermoplastic resin (A) is a polyimideresin, a polyamideimide resin, a polyesterimide resin, a polyetherimideresin or a polyamide resin.
 4. The adhesive film for semiconductor ofclaim 3, wherein the heat resistant thermoplastic resin (A) is apolyamideimide resin or a polyamide resin.
 5. A lead frame with adhesivefilm for semiconductor, comprising a lead frame and the adhesive filmfor semiconductor of claim 4 stuck to the lead frame.
 6. A semiconductordevice, containing a lead frame and a semiconductor element which arebonded to each other with the adhesive film for semiconductor of claim4.
 7. The adhesive film for semiconductor of claim 1, wherein the epoxyresin-curing agent (C) is a trisphenol compound represented by thefollowing general formula (a):

wherein R₁ to R₁₀ are each independently hydrogen, an alkyl group of 1to 10 carbon atoms, a cycloalkyl group of 5 to 10 carbon atoms, phenylgroup or hydroxyl group, and D is a tetravalent organic group.
 8. Theadhesive film for semiconductor of claim 7, wherein D in general formula(a) is


9. The adhesive film for semiconductor of claim 8, wherein R₅ in generalformula (a) is hydrogen or an alkyl group of 1 to 10 carbon atoms. 10.The adhesive film for semiconductor of claim 9, wherein ≡D—R₅ in generalformula (a) is


11. The adhesive film for semiconductor of claim 1, wherein the heatresistant thermoplastic resin has a glass transition temperature of 180to 250° C., a water absorption of 2.5% by weight or less, and a squeezelength of 1 mm or less.
 12. The adhesive film for semiconductor of claim11, wherein the water absorption and squeeze length of the heatresistant thermoplastic resin are respectively 2.0% by weight or lessand 0.5 mm or less.
 13. The adhesive film for semiconductor of claim 1,wherein the support film is an insulating heat resistant resin filmhaving a glass transition temperature of 250° C. or higher, a waterabsorption of 2% by weight or less and a thermal expansion coefficientof 3×10⁻⁵/° C. or less.
 14. The adhesive film for semiconductor of claim1, wherein the support film is an insulating heat resistant resinselected from the group consisting of a polyimide, a polyamide, apolysulfone, a polyphenylene sulfide, a polyetheretherketone, apolyallylate and a polycarbonate.
 15. A lead frame with adhesive filmfor semiconductor, comprising a lead frame and the adhesive film forsemiconductor of claim 1 stuck to the lead frame.
 16. A semiconductordevice, containing a lead frame and a semiconductor element which arebonded to each other with the adhesive film for semiconductor ofclaim
 1. 17. An adhesive film for semiconductor, which has a three-layerstructure consisting of a support film having each face coated with anadhesive layer, each adhesive layer containing (A) a heat resistantthermoplastic resin having a glass transition temperature of 130 to 300°C., (B) an epoxy resin and (C) a trisphenol compound as an epoxyresin-curing agent, wherein the adhesive film having the three-layerstructure has a water absorption of 3% by weight or less and a squeezelength of 2 mm or less.
 18. The adhesive film for semiconductor of claim16, wherein the adhesive film has a water absorption of 2.5% by weightor less and a squeeze length of 1 mm or less.
 19. The adhesive film forsemiconductor of claim 18, wherein the water absorption and squeezelength of the adhesive film are respectively 2.0% by weight or less and0.5 mm or less.
 20. The adhesive film for semiconductor of claim 17,wherein the heat resistant thermoplastic resin (A) is a polyimide resin,a polyamideimide resin, a polyesterimide resin, a polyetherimide resinor a polyamide resin.
 21. The adhesive film for semiconductor of claim20, wherein the heat resistant thermoplastic resin (A) is apolyamideimide resin or a polyamide resin.
 22. A lead frame withadhesive film for semiconductor, comprising a lead frame and theadhesive film for semiconductor of claim 17 stuck to the lead frame. 23.A lead frame with adhesive film for semiconductor, comprising a leadframe and the adhesive film for semiconductor of claim 22 stuck to thelead frame.
 24. A semiconductor device, containing a lead frame and asemiconductor element which are bonded to each other with the adhesivefilm for semiconductor of claim
 22. 25. A semiconductor device,containing a lead frame and a semiconductor element which are bonded toeach other with the adhesive film for semiconductor of claim 17.